Electrical apparatus, cooling system therefor, and electric vehicle

ABSTRACT

An inverter apparatus includes a liquid path in which cooling water flows, and in which the cooling water performs cooling at a cooling part located directly underneath the power circuit part of the inverter apparatus. The liquid path includes a first partial structure part formed between a feed pipe and the cooling part, and having a liquid path cross-sectional profile that is gradually reduced in the short-side direction of the cooling part and that is gradually enlarged in the long-side direction thereof; and a second partial structure part formed between the cooling part and a drain pipe, and having a liquid path cross-sectional profile that is gradually enlarged from the short-side of the cooling part and that is gradually reduced from the long-side thereof.

This application is a continuation of U.S. patent application Ser. No.11/476,629, filed Jun. 29, 2006, the entire disclosure of which isincorporated herein by reference, which is a continuation of U.S. patentapplication Ser. No. 10/803,929, filed Mar. 19, 2004, now U.S. Pat. No.7,090,044, which is a continuation of U.S. patent application Ser. No.10/417,339, filed Apr. 17, 2003, now U.S. Pat. No. 6,978,856, which inturn claims priority under 35 U.S.C. 119 of prior Japanese application2002-116274, filed Apr. 18, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates an electrical apparatus, a cooling systemtherefor, and electric vehicle inverter apparatus, and more particularlyto an inverter apparatus characterized by the liquid path structure inthe power circuit part in a liquid-cooling inverter.

2. Description of the Related Art

As an example of a conventional electric apparatus having a liquid pathincluding a space for allowing a cooling medium for cooling a heatingmember to flow therein, for example, a conventional liquid-coolinginverter, an inverter as shown in FIG. 8 in JP-A 10-22428, is known inwhich a plurality of rows of fins is formed on the surface of a module'ssubstrate adjacent to a cooling medium chamber, in which the fin rowsare arranged with the direction from the inlet of the cooling mediumflow toward the outlet thereof being the longitudinal direction, and inwhich the fins are formed as a contiguous sequence of fins in the flowdirection of the cooling medium. In such a case, it is also known that,because the width of the cooling medium chamber is wide with respect tothat of the cooling medium flow inlet, an accumulating part for thecooling medium is formed between the cooling medium flow inlet and thecooling medium chamber, in order to ensure a uniform flow rate of thecooling medium in the cooling medium chamber for achieving uniformcooling.

SUMMARY OF THE INVENTION

However, according to the examination by the present inventors, of thestructure disclosed in the JP-A 10-22428, it was found that thisstructure involves a problem of increasing the loss of pressure in theliquid path thereof. Specifically, the structure set forth in the JP-A10-22428 is one in which the depth of liquid path in the fin rows isless than that in the cooling medium flow inlet. In addition, respectiveaccumulating parts are provided between the inlet liquid path and theliquid path in the fin rows, and between the liquid path in the fin rowsand the outlet liquid path. Therefore, in the respective accumulatingparts, the liquid path depth steeply changes between the inlet liquidpath and the liquid path in the fin rows, thereby causing a loss ofpressure, and likewise, the liquid path depth steeply changes betweenthe liquid path in the fin rows and the outlet liquid path, therebyincurring a pressure loss. These pressure losses increase the load on apump for feeding the cooling medium into the liquid path. This raises aproblem of increasing the size of the pump.

Accordingly, it is an object of the present invention to provide aninverter apparatus having a liquid path structure that allows uniformcooling without the need for accumulating parts to thereby improve thethermal characteristic, and that reduces the loss of pressure in theliquid path.

The present invention provides an electric apparatus having a flowstructure for allowing uniform cooling to be achieved without the needfor accumulating parts, thereby improving thermal characteristic, andalso enables the pressure loss in the parts other than the cooling partto be reduced. Further, the present invention provides a cooling systemand an electric vehicle for the electrical apparatus.

To achieve the above-described object, the present invention provides aninverter apparatus having a liquid path comprising a space for allowinga cooling medium to flow therein, and a feed pipe and a drain pipe forallowing the cooling medium to enter into and drain out of the space,respectively. This liquid path includes a cooling part disposedimmediately underneath the heating part in the power circuit part of theinverter apparatus; a first partial structure part disposed between thefeed pipe and the cooling part, and having a liquid path cross-sectionalprofile that is gradually reduced in the short side direction of thecooling part and that is gradually enlarged in the long side directionthereof; and a second partial structure part disposed between thecooling part and the drain pipe, and having a liquid pathcross-sectional profile that is gradually enlarged from the short sideof the cooling part and that is gradually reduced from the long sidethereof.

By virtue of these features, the present invention allows uniformcooling to be achieved without the need for accumulating parts, therebyimproving thermal characteristic, and also enables the pressure loss inthe parts other than the cooling part to be reduced.

In the inverter apparatus according to the present invention, it ispreferable that each of the first and second partial structure parts beconstant in the rate of change of the length in the short side, and thateach of the first and second partial structure parts be constant in therate of change of the length in the long side.

In the inverter apparatus according to the present invention, it ispreferable that the first and second partial structure parts and thefeed and drain pipes be parallel with the cooling part, and that theangle formed between the peripheral wall of the cooling part and that ofeach of the partial structure parts be not more than 45 degrees.

In the inverter apparatus according to the present invention,preferably, the angle θ1 formed between the peripheral wall of the firstpartial structure part and that of the cooling part is smaller than theangle θ3 formed between the peripheral wall of the second partialstructure part and that of the cooling part.

In the inverter apparatus according to the present invention,preferably, each of the feed pipe and drain pipe is perpendicular to thecooling part.

In the inverter apparatus according to the present invention, it ispreferable that the feed pipe and drain pipe be located on the same sidewith respect to the inverter apparatus, wherein the angle θ5 formedbetween the peripheral wall of the feed pipe and that of the firstpartial structure part is not more than 45 degrees, and that the angleθ6 formed between the peripheral wall of the first partial structurepart and that of the cooling part be less than 90 degrees.

In the inverter apparatus according to the present invention,preferably, a plurality of inverter apparatuses is arranged on the sameplane.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing a module of an inverter apparatusaccording to a first embodiment of the present invention, FIG. 1B is aperspective plan view showing the liquid path part of this inverterapparatus, and FIG. 1C is a sectional view showing the overallconstruction of the inverter apparatus;

FIG. 2 is a perspective view showing the configuration of the liquidpath in the inverter apparatus according to the first embodiment;

FIG. 3 is a perspective view showing the configuration of the liquidpath in a conventional example;

FIG. 4A is a diagram showing variations in the liquid pathcross-sectional area of the liquid path structure used in the inverterapparatus according to the first embodiment of the present invention,and FIG. 4B is a diagram showing variations in the liquid pathcross-sectional area in the conventional example;

FIG. 5 is a diagram explaining the pressure loss value in the partsother than the cooling part when the liquid path structure used in theinverter apparatus according to the first embodiment is employed;

FIG. 6 is a perspective view showing the configuration of the liquidpath in an inverter apparatus according to a second embodiment of thepresent invention;

FIG. 7A is a plan view showing a module of an inverter apparatusaccording to a third embodiment of the present invention, FIG. 7B is aperspective plan view showing the liquid path part of this inverterapparatus, and FIG. 7C is a sectional view showing the overallconstruction of the inverter apparatus;

FIG. 8A is a plan view showing a module of an inverter apparatusaccording to a fourth embodiment of the present invention, FIG. 8B is aperspective plan view showing the liquid path part of this inverterapparatus, and FIG. 8C is a sectional view showing the overallconstruction of the inverter apparatus;

FIG. 9A is a perspective plan view showing the liquid path part of aninverter apparatus according to a fifth embodiment of the presentinvention, and FIG. 9B is a sectional view showing the overallconstruction of this inverter apparatus;

FIG. 10A is a perspective view showing the liquid path part of aninverter apparatus according to a sixth embodiment of the presentinvention, and FIG. 10B is a sectional view showing the overallconstruction of this inverter apparatus;

FIG. 11A is a perspective view showing the liquid path part of aninverter apparatus according to a seventh embodiment of the presentinvention, and FIG. 11B is a sectional view showing the overallconstruction of this inverter apparatus;

FIG. 12A is a perspective plan view showing the liquid path part of aninverter apparatus according to an eighth embodiment of the presentinvention, and FIG. 12B is a sectional view showing the overallconstruction of this inverter apparatus; and

FIG. 13A is a perspective plan view showing the liquid path part of aninverter apparatus according to a ninth embodiment of the presentinvention, and FIG. 13B is a sectional view showing the overallconstruction of this inverter apparatus.

FIG. 14 is a block diagram of a cooling system for a controller(inverter apparatus) and electric motor of an electric vehicleincorporating any of the above-described inverter apparatuses.

FIG. 15 is a plan view of the construction of an electrical apparatusdrive system equipped with the above-described cooling system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The construction of an inverter apparatus according to an firstembodiment of the present invention will be described below inconnection with FIGS. 1 to 5.

First, references will be made to the overall construction of theinverter apparatus according to the first embodiment with reference toFIG. 1. The liquid-cooling inverter according to this embodiment is usedas an on-board inverter for vehicles such as vehicles contributingenvironmental safeguard.

FIG. 1A is a plan view showing a module with six arms (upper and lowerarms in each of the U, V, and W phases) of the inverter apparatusaccording to the first embodiment of the present invention, and FIG. 1Bis a perspective plan view showing the liquid path part of this inverterapparatus. FIG. 1C is a sectional view showing the overall constructionof the inverter apparatus, the sectional view being taken along the lineA-A′ in FIG. 1B.

As shown in FIG. 1A, the module 100 includes semiconductor chips 103 and104, substrates 102, and a copper base 101. Each of the semiconductorchips 103 and each of the semiconductor chips 104 are typicallyconstituted of an IGBT (Insulated Gate Bipolar Transistor) and an FWD(Free Wheeling Diode), respectively. The inverter apparatus convertsdirect-current power supplied by a direct-current power source, such asa battery, into alternating-current power, and supplies the obtainedalternating-current power to an electric motor to drive it, with thesemiconductor chips 103 thereof performing a function of switching byPWM (Pulse Width Modulation) control or the like.

In the illustrated example, six substrates 102 are mounted on the copperbase 101, thereby constituting 6 arm module. Three semiconductor chips103 and two semiconductor chips 104 are mounted on each of thesubstrates 102. The planar size of the substrate 102 is, e.g.,approximately 27 mm □ 55 mm. The planar size of the semiconductor chip103 is, e.g., approximately 9 mm square. The planar size of thesemiconductor chip 104 is, e.g., approximately 6 mm square. Thesubstrate 102 is formed by solder-brazing a copper foil over each of thefront and rear surfaces of an aluminum nitride plate.

As shown in FIG. 1C, the semiconductor chips 103 and 104 are mounted oneach of the substrates 102 via solder 106. Each of the substrate 102 ismounted on the copper base 101 via solder 107. The planar size of thecopper base 101 is, e.g., approximately 100 mm □ 230 mm. Screw holes 105for screwing are formed in the copper base 101, and the size of thescrew hole is approximately M6. Using screws 111, the module 100 isfastened, via grease, to the case 110 formed by aluminum die-casting.

As illustrated in FIG. 1C, a liquid path 120 indicated by hatching isformed within the case 110. The liquid path 120 has a shape as shown inFIGS. 1C and 1B. As shown in FIG. 1C, in the central part of the case110, fins 109 integrally formed with the case 110 are provided at thepart (referred to as a “cooling part”) below the place where thesemiconductor chips 103 and 104 are mounted.

As shown in FIG. 1B, the fins 109 are formed in parallel with thelongitudinal direction of the liquid path 120. In the illustratedsample, there are provided thirteen fins 109 parallel with one another.The width Wf1 of each of the fins is, e.g., 2.5 mm.

As illustrated in FIG. 1B, the module 100 is installed into the liquidpath at the location indicated by thick dotted lines. The module 100 iscooled by supplying an LLC (Long Life Coolant), which is cooling-water,from an electric water pump (not shown) to the liquid path 120. Themaximum flow rate of the electric water pump is 20 liters per minute,and the maximum pressure loss thereof is approximately 14 kPa.

A feed tube to be connected to a radiator is connected to the left endof the liquid path 120. The liquid path 120 comprises a feed pipe 112,partial structure pipe 113, cooling part 114, partial structure pipe115, and drain pipe 116. An inter-fin liquid path 118 is formed in thecentral part of the cooling part 114. A drain tube to be connected tothe radiator is connected to the right end of the water drain pipe 116.

The configuration of the liquid path 120 will be further described withreference to FIG. 2.

FIG. 2 is a perspective view showing the configuration of the liquidpath in the inverter apparatus according to the first embodiment.

A feed tube to be connected to the radiator is connected to the feedpipe inlet 200. The diameter R1 of the feed pipe inlet 200 is, e.g., 17mm. The feed pipe 112 has a quadrangular prism shape. The height H1thereof is, e.g., 17 mm, the width W1 thereof is, e.g., 17 mm, and thelength L1 thereof is, e.g., 10 mm.

The liquid path cross-sectional profile in the partial structure pipe113 extending from the feed pipe 112 up to the cooling part 114,substantially has a shape that is gradually reduced in the short sidedirection of the cooling part 112, that is gradually enlarged in thelong side direction thereof, and that connects the feed pipe 112 and thecooling part 114. Namely, the partial structure pipe 113 is configuredto gradually widen from the liquid path cross-section 202 up to theliquid path cross-section 203 in the direction of the liquid path width(long side), and gradually narrow in the direction of the liquid pathdepth (short side). The width of the liquid path cross-section 202 isequal to the width W1, and it is, e.g., 17 mm. The width W2 of theliquid path cross-section 203 is, e.g., 60 mm. The length L2 of thepartial structure pipe 113 is, e.g., 23 mm. The rate of change inexpansion of the partial structure pipe 113 in the liquid path widthdirection and the rate of change in reduction in the liquid path depthdirection are each substantially constant. The angle of the partialstructure pipe 113 decreasing in the liquid path depth direction, thatis, the angle θ1 formed between the peripheral wall of the cooling part114 and that of the partial structure pipe 113, is 30 degrees. It isdesirable that this angle θ1 be not more than 45 degrees in order toreduce the loss of pressure. On the other hand, the angle of the partialstructure pipe 113 increasing in the liquid path width direction, thatis, the angle θ2 formed between the peripheral wall of the cooling part114 and that of the partial structure pipe 113, is 30 degrees. It isdesirable that this angle θ2 be not more than 45 degrees in order toreduce the pressure loss.

In the cooling part 114, there is provided the inter-fin liquid path 118having therein fins 109 integrally molded with the case 110. The finwidth Wf1 of each of the fins 109 is, e.g., 2.5 mm, the spacing Wf2between adjacent fins is, e.g., 2 mm, and the fin height is, e.g., 5 mm.When the flow rate is 20 liters per minute, the flow speed in theinter-fin liquid path 118 is approximately 2.5 m/s. The length L4 of theinter-fin liquid path 118 is, e.g., 150 mm, and each of the lengths L3and L5 of the portions of the cooling part 114, located before and afterthe inter-fin eater path is, e.g., 10 mm.

The LLC passed through the fins 109 is narrowed in the partial structurepipe 115 in the liquid path width direction, from the liquid pathcross-section 204 up to the liquid path cross-section 205, at an angleof 30 degrees, and it is gradually widened in the liquid path depthdirection. Furthermore, the LLC flows from the drain pipe 116 toward thedrain pipe outlet 201 with a diameter of 17φ. It is desirable that theangle of the partial structure pipe 115 increasing in the liquid pathdepth direction be not more than 45 degrees. The length L6 of thepartial structure pipe 115 is, e.g., 23 mm. The width and height of theliquid path cross-section 204 are made equal to those of the liquid pathcross-section 203, and the width and height of the liquid pathcross-section 205 are made equal to those of the liquid pathcross-section 202. The width W4 of the drain pipe 116 is, e.g., 17 mm,and the height H4 thereof is, e.g., 17 mm.

In order to reduce the loss of pressure in the liquid path, it isdesirable that the angle θ1 formed by the partial structure pipe 113 andthe cooling part, be smaller than the angle θ3 formed by the partialstructure pipe 115 and the cooling part. Specifically, in theabove-described example, the angle θ1 is 30 degrees and the angle θ3 isalso 30 degrees, but it is desirable to change the angle θ1 into, e.g.,20 degrees. Thereby, the loss of pressure can be more reduced althoughthe entire length of the liquid path lengthens. When attempting toreduce the entire length of the liquid path, with the angle θ1 as wellas the angle θ3 being 30 degrees, it is recommended that the angle θ3 ischanged into 40 degrees. This would reduce the length of the liquid pathand allow the size-reduction of the inverter apparatus, although theloss of pressure slightly increases. Meanwhile, because the case 110 isa casting, each of the corners thereof has a rounded corner withapproximately 1 mm radius of curvature, and also the case 110 actuallyhas a gradient of a few degrees for chamfering.

Here, the structure of the liquid path in the conventional example willbe described with reference to FIG. 3.

FIG. 3 is a perspective view showing the configuration of the liquidpath in the conventional example.

The liquid path 300 having the liquid path structure shown in FIG. 3enters from a feed pipe inlet 200 into a partial structure part 301through a liquid path inlet 112. From a liquid path cross-section 305 upto a liquid path cross-section 306, the liquid path 300 widens in theliquid path width direction, but it does not change in the liquid pathdepth direction. Likewise, with regard to the drain pipe side, from aliquid path cross-section 307 up to a liquid path 308, the liquid path300 narrows in the liquid path width direction, but it does not changein the liquid path depth direction. On the feed pipe side, there existsan accumulating part 303 between a partial structure part 301 and acooling part 114. Similarly, on the drain pipe side, there exists anaccumulating part 304 between the cooling part 114 and a partialstructure part 302. The LLC passes through the partial structure part302 and the drain pipe 116, and is drained from the drain pipe outlet201.

Next, with reference to FIGS. 4A and 4B, variations in the liquid pathcross-sectional area when the liquid path structure according to thefirst embodiment of the present invention is used, will be described incomparison with the conventional example.

FIG. 4A is a diagram showing variations in the liquid pathcross-sectional area of the liquid path structure used in the inverterapparatus according to the first embodiment of the present invention,and FIG. 4B is a diagram showing variations in the liquid pathcross-sectional area in the conventional example.

In FIG. 4A, the abscissa axis denotes a position X of the liquid path120 in the longitudinal direction. The ordinal axis denotes a liquidpath cross-sectional area S. In FIG. 4A, a position x1 denotes theposition of the feed pipe inlet 200 shown in FIG. 2. When the liquidpath cross-sectional profile changes from 17φ into 17 mm square at theposition x1, the liquid path cross-sectional area steeply changes fromS2 (227 mm²) into S3 (289 mm²). A position x2 denotes the position of aliquid path cross-section 202 in FIG. 2. A position x3 denotes theposition of a liquid path cross-section 203 shown in FIG. 2. In therange from the position x2 to the position x3, the liquid pathcross-sectional area gradually changes from S3 (289 mm²) into S4 (300mm²) because the partial structure pipe 113 is employed here. The rangefrom a position x4 to a position x5 denote the positional range wherethe inter-fin liquid path 118 is formed. At the position x4, the liquidpath cross-sectional area steeply changes from S4 (300 mm²) into S1 (150mm²). A position x6 denotes the position of the liquid pathcross-section 204 in FIG. 2, and a position x7 denotes the position ofthe liquid path cross-section 205 in FIG. 2. In the range from theposition x6 to the position x7, the liquid path cross-sectional areagradually changes from S4 (300 mm²) into S3 (289 mm²) because thepartial structure pipe 115 is employed here. A position x8 denotes theposition of the drain pipe outlet 201 in FIG. 2. When the liquid pathcross-sectional profile changes from 17 mm square into 17φ at theposition x8, the liquid path cross-sectional area steeply changes fromS3 (289 mm²) into S2 (227 mm²).

In FIG. 4B, a position x2 denotes the position of a liquid pathcross-section 305 shown in FIG. 3. A position x9 denotes the position ofa liquid path cross-section 306 in FIG. 3. At the positions from x2 tox9, the liquid path cross-sectional area changes from S3 (289 mm²) intoS5 (1020 mm²). A position x3 denotes the position of the inlet of thecooling part 114. At the position x3, the liquid path cross-sectionalarea steeply changes from S5 (1020 mm²) into S4 (300 mm²). Likewise, aposition x6 denotes the position of the outlet of the cooling part 114in FIG. 3, a position x10 denotes the position of a liquid pathcross-section 307, and a position x7 denotes the position of a liquidpath cross-section 308. At the positions from x10 to x7, the liquid pathcross-sectional area steeply changes from S5 (1020 mm²) into S3 (289mm²).

Next, with reference to FIG. 5, the loss of pressure in the parts otherthan the cooling part when the liquid path structure according to thisembodiment is used, will be described in comparison with theconventional example.

In FIG. 5, the pressure loss in the parts other than the cooling partwhen the liquid path structure used in the inverter apparatus accordingto the first embodiment of the present invention is employed, is shownwith respect to the pressure loss in the conventional example. Theordinate axis denoted pressure loss value (kPa) in the parts other thanthe cooling part.

In FIG. 5, X represents a pressure loss value in the liquid pathstructure of the conventional example. Due to the existence of thepartial structure parts 301 and 302 and the accumulating parts 303 and304, a steep change occurs in the liquid path cross-sectional profileand cross-sectional area between these pipes, accumulating parts, andthe cooling part 114. The pressure loss value in the parts other thanthe cooling part 114 shown in FIG. 3 was measured as 2.4 kPa. Thispressure loss value does not contribute to heat transmission at all. Itis desirable to minimize the pressure loss value.

On the other hand, Y in FIG. 5 represents a pressure loss value in thecase of the liquid path structure according to this embodiment. Bygradually changing the partial structure pipes 113 and 115 in the widthand depth directions of the liquid path, it is possible to avoid theoccurrence of steep changes in the liquid path cross-sectional profileand cross-sectional area between the partial structure pipes 113 and 115and the cooling part 114, and thereby to reduce the loss of pressure.The pressure loss value in the parts other than the cooling part 114 inthis example was measured as 0.5 kPa. Thus, the pressure loss value inthis embodiment can be reduced by a factor of about five, as comparedwith that of 2.4 kPa in the conventional example shown in FIG. 3. Thepressure loss values of the cooling parts 114 shown in FIG. 2 (thepresent embodiment) and FIG. 3 (the conventional example) are the same,that is, the heat radiation capacities of the modules 100 are equal toeach other.

As shown in FIG. 2, the partial structure pipe 113 is configured togradually change in the width and depth directions of the liquid path,and therefore, even when the width W2 (=60 mm) of the cooling part iswide with respect to a feed tube (17φ), it is possible to ensure auniform flow rate of the cooling medium (cooling water) in the coolingpart 114, and thereby to achieve uniform cooling. That is, according tothe present embodiment, the loss of pressure can be reduced withoutdeteriorating the heat transmission characteristic of the liquid path.This allows the size-reduction of the pump. Also, since the reduction inpressure loss enables the inverter to be cooled more efficiently, thesize-reduction of the inverter can be implemented.

As described above, according to the present embodiment, in the liquidpath extending from the feed pipe inlet up to the cooling part, there isprovided a partial structure part having a cross-sectional profile thatis gradually reduced in the short side direction of the cooling part andthat is gradually enlarged in the long side direction thereof, and inthe liquid path extending from the cooling part up to the drain pipeoutlet, there is provided a partial structure part having across-sectional profile that is gradually enlarged from the short sideof the cooling part and that is gradually reduced from the long sidethereof. This makes it possible to achieve uniform cooling in thecooling part, thereby improving the thermal characteristic, and also toreduce the pressure loss in the parts other than the cooling part.

Next, the construction of an inverter apparatus according to a secondembodiment of the present invention will be described with reference toFIG. 6. The overall construction of the liquid-cooling inverteraccording to this embodiment is the same as that shown in FIG. 1.

FIG. 6 is a perspective view showing the configuration of the liquidpath in the inverter apparatus according to the second embodiment. InFIG. 6, the same reference numerals denote the same parts as those inFIG. 2.

A feed pipe 501 and drain pipe 504 constituting a liquid path 500,respectively, are cylinders having the same diameters as those of thefeed pipe inlet 200 and the drain pipe outlet 201. A partial structurepart 502 is configured to be gradually enlarged from a liquid pathcross-section 505 up to a liquid path cross-section 506 in the liquidpath width direction, and gradually reduced in the liquid path depthdirection. On the other hand, a partial structure part 503 is configuredto be gradually reduced from a liquid path cross-section 507 up to aliquid path cross-section 508 in the liquid path width direction, andgradually enlarged in the liquid path depth direction. The partialstructure parts 502 and 503 may have a nested configuration, oralternatively may be a combination of a half cylinder and a rectangularparallelepiped by providing an opening part only on the surfacebordering on the module.

In this embodiment, the pressure loss value can be reduced more than thecase in the structure shown in FIG. 2. This is because a feed pipe 501has a circular cross-section with the same diameter as that of the feedpipe connected to the radiator, thereby causing no loss of pressure inthis part, and because the partial structure part 502 has a structurehas a cross-section that is gradually changed, thereby reducing the lossof pressure. The pressure loss value in the parts other than the coolingpart 114 was measured as 0.3 kPa. Thus, the present liquid pathstructure can make the pressure loss value lower than the pressure lossvalue of 0.5 kPa in the structure shown in FIG. 2. This allows thesize-reduction of the pump or inverter to be implemented.

As described above, according to the present embodiment, by providingrespective partial structure parts in the liquid path extending from thefeed pipe inlet up to the cooling part, and in the liquid path extendingfrom the cooling part up to the drain pipe outlet, it is possible toachieve uniform cooling in the cooling part, thereby improving thethermal characteristic, and also to reduce the pressure loss in theparts other than the cooling part. Furthermore, by forming each of thefeed pipe and drain pipe into a cylindrical shape, the loss of pressurecan be more reduced.

Next, the construction of the inverter apparatus according to a thirdembodiment of the present invention will be described with reference toFIGS. 7A to 7C.

FIG. 7A is a plan view showing a module with six arms (upper and lowerarms in each of the U, V, and W phases) of an inverter apparatusaccording to the third embodiment, and FIG. 7B is a perspective planview showing the liquid path part of the inverter apparatus according tothis embodiment. FIG. 7C is a sectional view showing the overallconstruction of the inverter apparatus according to this embodiment, thesectional view being taken along the line B-B′ in FIG. 7B. In FIG. 7A to7C, the same reference numerals denote the same parts as those in FIG.1.

The inverter apparatus according to this embodiment is used as awater-cooling inverter having the configuration of a base-direct-coolingmodule with fins. Specifically, fins 602 are integrally formed with acopper base 601. An opening part is formed at the center of the upperpart of the case 110. A liquid path 603 is formed by inserting the fins602 into the aforementioned opening part, and fastening a module 600 tothe case 110 using screws 111. The size of the fins 602 is equivalent tothat of the fins 109 shown in FIG. 1. In this manner, by forming thefins 602 integrally with the copper base 601, the inverter apparatusaccording to this embodiment can improve the cooling efficiency as adirect cooling system that directly applies cooling water to the module600. In general, the module 600 is prevented from water leakage from theliquid path to the high voltage part thereof by screwing and an O-ring(not shown). However, the module may instead be prevented from beingcovered with water by welding or FSW (Friction Stirring Welding).

The liquid path parts 112, 113, 114, 115, and 116 are substantially thesame as those shown in FIGS. 1 and 2, in which the liquid path parts 113and 115 are provided as partial structure parts. As a result of formingthe liquid path using the copper base 601, the width of the liquid pathbecomes narrowed by one plate thickness t1 (e.g., 2 mm) at the end part110A adjacent to the central part of the upper plate of the case 110,there is a risk of causing a loss of pressure. Therefore, a round cornerR117 is provided at the part corresponding to the end part 110A in orderto reduce the pressure loss.

In the liquid path structure having the shape shown in FIG. 7, thepressure loss value in the parts other than the cooling part 114 wasmeasured as 0.6 kPa. Although the pressure loss value in this case ishigher by about 0.1 kPa than that in the structure shown in FIG. 2, thepresent liquid path structure can reduce the pressure loss value withrespect to the conventional structure. This allows the size-reduction ofthe pump or inverter. In addition, it is recognized that the adoption ofthe direct cooling system improves the cooling efficiency.

As described above, according to the present embodiment, by providingrespective partial structure parts in the liquid path extending from thefeed pipe inlet up to the cooling part, and in the liquid path extendingfrom the cooling part up to the drain pipe outlet, it is possible toachieve uniform cooling in the cooling part, thereby improving thethermal characteristic, and also to reduce the pressure loss in theparts other than the cooling part. Furthermore, by adopting the directcooling system, the cooling efficiency can be improved.

Next, the construction of the inverter apparatus according to a fourthembodiment of the present invention will be described with reference toFIGS. 8A to 8C.

FIG. 8A is a plan view showing a module with six arms (upper and lowerarms in each of the U, V, and W phases) of an inverter apparatusaccording to the fourth embodiment of the present invention, and FIG. 8Bis a perspective plan view showing the liquid path part of the inverterapparatus according to this embodiment. FIG. 8C is a sectional viewshowing the overall construction of the inverter apparatus according tothis embodiment, the sectional view being taken along the line C-C′ inFIG. 8B. In FIG. 8A to 8C, the same reference numerals denote the sameparts as those in FIG. 1.

The inverter apparatus according to this embodiment is used as awater-cooling inverter having the configuration of a base-direct-coolingmodule without fins. Specifically, the copper base 100 is a flat platewithout fins. The constructions other than the copper base 100 is thesame as those shown in FIG. 6. As a cooling system, a direct coolingsystem is used also in the case. A liquid path 700 is formed by joiningthe module 100 to the case 110 by screwing or welding. The liquid pathdepth H6 in a cooling part 701 is. e.g., approximately 2 mm. When theflow rate is 20 liters per minute, the flow speed in the cooling part701 is approximately 2.5 m/s.

In the liquid path structure having the shape shown in FIG. 8, thepressure loss value in the parts other than the cooling part 114 wasmeasured as 1 kPa. Although the pressure loss value in this case ishigher than the structure shown in FIG. 7, the present liquid pathstructure can reduce the pressure loss value with respect to theconventional structure. This allows the size-reduction of the pump orinverter. In addition, it is recognized that the adoption of the directcooling system improves the cooling efficiency.

As described above, according to the present embodiment, by providingrespective partial structure parts in the liquid path extending from thefeed pipe inlet up to the cooling part, and in the liquid path extendingfrom the cooling part up to the drain pipe outlet, it is possible toachieve uniform cooling in the cooling part, thereby improving thethermal characteristic, and also to reduce the pressure loss in theparts other than the cooling part. Furthermore, the cooling efficiencycan be improved by adopting the direct cooling system.

Next, the construction of the inverter apparatus according to a fifthembodiment of the present invention will be described with reference toFIGS. 9A and 9B.

FIG. 9A is a perspective plan view showing the liquid path part of theinverter apparatus according to this embodiment. FIG. 9B is a sectionalview showing the overall construction of the inverter apparatusaccording to this embodiment, the sectional view being taken along theline D-D′ in FIG. 9A. In FIGS. 9A and 9B, the same reference numeralsdenote the same parts as those in FIG. 1.

The inverter according to this embodiment is a two-inverter systemhaving liquid paths that are connected end to end parallel with eachother. The planar configuration of the inverter apparatus according tothis embodiment is similar to that shown in FIG. 1A, but in thisembodiment, two modules are arranged in series on the same plane in theliquid path flow direction.

In a liquid path 800, the cooling water flows from a pre-stage coolingpart 114 toward a post-stage cooling part 802 through liquid path 801.The size of fins 803 is equivalent to that of the fins 109. The fins 109and fins 803 may be integrally connected with each other in midway. Thefeed and drain pipes 112 and 116 may each be disposed substantiallyperpendicularly to the cooling part 114.

When the cooling water was fed at a flow rate of 20 liters per minute,the pressure loss in the other parts other than the cooling parts 114and 802 was measured as 1.5 kPa. This is because the pressure loss inthe liquid path 801 part is large. However, when the conventionalstructure shown in FIG. 3 was applied to a two-inverter type, thepressure loss value thereof was found to be 3.4 kPa, and therefore, itcan be seen that the present liquid path structure can reduce thepressure loss with respect to the conventional structure. Meanwhile,when the flow rate is likely to exceed the supply capacity of the pump,the flow rate should be reduced to one corresponding to the permissibleupper limit of pressure loss. In the present structure also, thesize-reduction of the inverter can be implemented. Here, as aliquid-cooling system, an indirect cooling system is used, but a directcooling system as shown in FIGS. 7A to 7C and FIGS. 8A to 8C may insteadbe employed.

As described above, according to the present embodiment, by providingrespective partial structure parts in the liquid path extending from thefeed pipe inlet up to the cooling part, and in the liquid path extendingfrom the cooling part up to the drain pipe outlet, it is possible toachieve uniform cooling in the cooling part, thereby improving thethermal characteristic, and also to reduce the pressure loss in theparts other than the cooling part.

Next, the construction of the inverter apparatus according to a sixthembodiment of the present invention will be described with reference toFIGS. 10A and 10B.

FIG. 10A is a perspective view showing the liquid path part of theinverter apparatus according to this embodiment. FIG. 10B is a sectionalview showing the liquid path part of the inverter apparatus according tothis embodiment, the sectional view being taken along the line E-E′ inFIG. 10A. In FIGS. 10A and 10B, the same reference numerals denote thesame parts as those in FIG. 1.

In this embodiment, the feed and drain pipes are each disposedsubstantially perpendicularly to the cooling part, and generally, thewater pipe cross-sectional profile from the feed pipe up to the coolingpart is gradually reduced in the short-side direction of the connectingcross-section between the partial structure part and the cooling part,and is gradually enlarged in the long-side direction thereof. On theother hand, generally, the water pipe cross-sectional profile from thecooling part up to the drain pipe is gradually enlarged from theshort-side of the connecting cross-section between the cooling part andthe partial structure part, and is gradually reduced from the long-sidethereof.

In the construction shown in FIG. 10, the parts other than the liquidpath 900 are the same as those in FIG. 1. The feed pipe 901 and thedrain pipe 904 are each disposed substantially perpendicularly to thecooling part 114. Between the feed pipe 901 and the cooling part 114,there is provided a partial structure part 902 that is enlarged from theliquid path cross-section 905 up to the liquid path cross-section 906 inthe liquid path width (long-side) direction, and that is reduced in theliquid path depth (short-side) direction. Likewise, between the coolingpart 114 and the drain pipe 904, there is provided a partial structurepart 903 that is reduced from the liquid path cross-section 907 up tothe liquid path cross-section 908 in the liquid path width (long-side)direction, and that is enlarged in the liquid path depth (short-side)direction.

In the liquid path structure having the shape shown in FIG. 10, thepressure loss value in the parts other than the cooling part 114 wasmeasured as 1.7 kPa. Thus, the present liquid path structure can reducethe pressure loss value by about 30% than the conventional structureshown in FIG. 3. This enables the size-reduction of the pump or theinverter to be realized. Also, disposing the feed pipe side and thedrain pipe side perpendicularly to the cooling part allows the area ofthe liquid-cooling inverter to become smaller than that of theconventional structure, resulting in a size-reduced inverter. Inaddition, because the feed and drain pipes are located on the same sidewith respect to the inverter, a high degree of flexibility in design isprovided.

As described above, according to the present embodiment, by providingrespective partial structure parts in the liquid path extending from thefeed pipe inlet up to the cooling part, and in the liquid path extendingfrom the cooling part up to the drain pipe outlet, it is possible toachieve uniform cooling in the cooling part, thereby improving thethermal characteristic, and also to reduce the pressure loss in theparts other than the cooling part.

Next, the construction of the inverter apparatus according to a seventhembodiment of the present invention will be described with reference toFIGS. 11A and 11B.

FIG. 11A is a perspective view showing the liquid path part of theinverter apparatus according to this embodiment. FIG. 11B is a sectionalview showing the liquid path part of the inverter apparatus according tothis embodiment, the sectional view being taken along the line F-F′ inFIG. 11A. In FIGS. 11A and 11B, the same reference numerals denote thesame parts as those in FIG. 1.

As in the case of the sixth embodiment shown in FIGS. 10A and 10B, inthe present embodiment, the feed and drain pipes are each disposedsubstantially perpendicularly to the cooling part. The constructionsother than the construction of a liquid path 1000 is the same as thosein FIG. 1. Each of the feed pipe 1001 and the drain pipe 1004 issubstantially normal to the cooling part 114, as described above.Between the feed pipe 1001 and the cooling part 114, there is provided apartial structure part 1002 that is enlarged from the liquid pathcross-section 1005 up to the liquid path cross-section 1006 in theliquid path width direction, and that is reduced in the liquid pathdepth direction. Likewise, between the cooling part 114 and the drainpipe 1004, there is provided a partial structure part 1003 that isreduced from the liquid path cross-section 1007 up to the liquid pathcross-section 1008 in the liquid path width direction, and that isenlarged in the liquid path depth direction.

The present embodiment is different from the sixth embodiment shown inFIG. 10 in the angle of the peripheral wall of each of the partialstructure parts 1002 and 1003 with respect to the cooling part 114.Specifically, the angle θ5 formed between the peripheral wall of thefeed pipe 1001 and that of the partial structure part 1002 is 45degrees. Also, the angle θ6 formed between the peripheral wall of thepartial structure part 1002 and that of the cooling part 114 is 45degrees. Thereby, the cooling water entered in the feed pipe inlet 200turns the flow direction thereof by an angle of approximately 45 degreesbetween the feed pipe 1001 and the partial structure part 1002, andfurther, it turns the flow direction thereof by an angle ofapproximately 45 degrees between the partial structure part 1002 and thecooling part 114, thus flowing into the cooling part 114. Likewise, withregard to the drain pipe side, the cooling water turns the flowdirection thereof by an angle of approximately 45 degrees between thecooling part 114 and the partial structure part 1003, and further, itturns the flow direction thereof by an angle of approximately 45 degreesbetween the partial structure part 1003 and the drain pipe 1004, thusflowing out from the drain pipe outlet 201.

As described above, in this embodiment, by dividing the change (vectorchange) in the flow direction between the feed and drain pipes 1001 and1004 and the cooling part 114 into two steps, and setting one-stepvector change to 45 degrees, the occurrence of pressure loss caused by asteep vector change is prevented. It is desirable that the angle θ5formed between the peripheral wall of the feed pipe 1001 and that of thepartial structure part 1002 be not more than 45 degrees. Also, it isdesirable that the angle θ6 formed between the peripheral wall of thefeed pipe 1002 and that of the cooling part 114 be less than 45 degrees.

In the present embodiment, the pressure loss value in the parts otherthan the cooling part 114 was measured as 1.1 kPa. Thus, the presentliquid path structure can reduce the pressure loss value with respect tothe example shown in FIG. 10. Also, disposing the feed pipe side and thedrain pipe side perpendicularly to the cooling part allows the area ofthe liquid-cooling inverter to be smaller than that of the conventionalstructure, resulting in a size-reduced inverter. In addition, becausethe feed and drain pipes are located on the same side with respect tothe inverter, a higher degree of flexibility in design is provided.

As described above, according to the present embodiment, by providingrespective partial structure parts in the liquid path extending from thefeed pipe inlet up to the cooling part, and in the liquid path extendingfrom the cooling part up to the drain pipe outlet, it is possible toachieve uniform cooling in the cooling part, thereby improving thethermal characteristic, and also to reduce the pressure loss in theparts other than the cooling part.

Next, the construction of the inverter apparatus according to an eighthembodiment of the present invention will be described with reference toFIGS. 12A and 12B.

FIG. 12A is a perspective plan view showing the liquid path part of theinverter apparatus according to this embodiment. FIG. 12B is a sectionalview showing the overall construction of the inverter apparatusaccording to this embodiment, the sectional view being taken along theline G-G′ in FIG. 12A. In FIGS. 12A and 12B, the same reference numeralsdenote the same parts as those in FIG. 1.

The inverter according to this embodiment is a two-inverter systemhaving liquid paths that are serially connected into an L-shape. Theplanar configuration of the inverter apparatus according to thisembodiment is similar to that shown in FIG. 1A, but in this embodiment,two modules exist on the same plane. In a liquid path 1100, two modulesare arranged in series in the flow direction, and form a substantiallyL-shape between the two inverters.

In the liquid path 1100, the cooling water flows from a pre-stagecooling part 114 toward a post-stage cooling part 1102 through a liquidpath 1101. The size of fins 1103 is equivalent to that of the fins 109.The fins 109 and fins 1103 may be integrally connected with each otherin midway. The feed and drain pipes 112 and 116 and the partialstructure parts 113 and 115 may each be disposed substantiallyperpendicularly to the cooling part 114. Here, as a liquid-coolingsystem, an indirect cooling system is used, but a direct cooling systemas shown in FIGS. 7A to 7C and FIGS. 8A to 8C may instead be employed.

When the cooling water was fed at a flow rate of 20 liters per minute,the pressure loss in the other parts other than the cooling parts 114and 1102 was measured as 3.2 kPa. Thus, the present liquid pathstructure can reduce the pressure loss with respect to the case wherethe conventional structure is applied to the two-inverter type shown inFIG. 3. Meanwhile, when the flow rate is likely to exceed the supplycapacity of the pump, the flow rate should be reduced to onecorresponding to the permissible upper limit of pressure loss. In thepresent liquid path structure also, the size-reduction of the invertercan be implemented.

As described above, according to the present embodiment, by providingrespective partial structure parts in the liquid path extending from thefeed pipe inlet up to the cooling part, and in the liquid path extendingfrom the cooling part up to the drain pipe outlet, it is possible toachieve uniform cooling in the cooling part, thereby improving thethermal characteristic, and also to reduce the pressure loss in theparts other than the cooling part.

Next, the construction of the inverter apparatus according to a ninthembodiment of the present invention will be described with reference toFIGS. 13A and 13B.

FIG. 13A is a perspective plan view showing the liquid path part of theinverter apparatus according to this embodiment. FIG. 13B is a sectionalview showing the overall construction of the inverter apparatusaccording to this embodiment, the sectional view being taken along theline H-H′ in FIG. 13A. In FIGS. 13A and 13B, the same reference numeralsdenote the same parts as those in FIG. 1.

The inverter according to this embodiment is a two-inverter systemhaving liquid paths that are serially connected into a U-shape. Theplanar configuration of the inverter apparatus according to thisembodiment is similar to that shown in FIG. 1A, but in this embodiment,two modules exist on the same plane. In a liquid path 1200, two modulesare arranged in series in the flow direction, and form a substantiallyU-shape between the two inverters.

In the liquid path 1200, the cooling water flows from a pre-stagecooling part 114 toward a post-stage cooling part 1202 through a liquidpath 1201. The size of fins 1203 is equivalent to that of the fins 109.The fins 109 and fins 1203 may be integrally connected with each otherin midway. The feed and drain pipes 112 and 116 and the partialstructure parts 113 and 115 may each be disposed substantiallyperpendicularly to the cooling part 114. Here, as a liquid-coolingsystem, an indirect cooling system is used, but a direct cooling systemas shown in FIGS. 7A to 7C and FIGS. 8A to 8C may instead be employed.

When the cooling water was fed at a flow rate of 20 liters per minute,the pressure loss in the other parts other than the cooling parts 114and 1202 was measured as 4.2 kPa. Thus, the present liquid pathstructure can reduce the pressure loss with respect to the case wherethe conventional structure is applied to the two-inverter type shown inFIG. 3. Meanwhile, when the flow rate is likely to exceed the supplycapacity of the pump, the flow rate should be reduced to onecorresponding to the permissible upper limit of pressure loss. In thepresent liquid path structure also, the size-reduction of the invertercan be implemented.

As is evident from the foregoing, according to the present embodiment,by providing respective partial structure parts in the liquid pathextending from the feed pipe inlet up to the cooling part, and in theliquid path extending from the cooling part up to the drain pipe outlet,it is possible to achieve uniform cooling in the cooling part, therebyimproving the thermal characteristic, and also to reduce the pressureloss in the parts other than the cooling part.

FIG. 14 shows a cooling system for a controller (inverter apparatus) andelectric motor of an electric vehicle, such as an electric car or hybridcar, incorporating any of the above-described inverter apparatuses. Thecooling system is formed by connecting, using a cooling pipe 5, anelectric motor 2 for driving an axle, a controller 1 (inverterapparatus) for controlling the output of the electric motor 2, aradiator 3 for cooling a cooling medium, and an electric pump 4. Anantifreeze solution as a cooling medium is sealed in the cooling pipe 5.A radiator fan motor 6 for forcibly cooling the cooling medium isattached to the side surface of the radiator 3. In the above-describedconstruction, the amount of heat generated by the controller 1 (inverterapparatus) and that generated by the electric motor 2 are substantiallythe same. However, the heating value of electronic components, such astransistors, capacitors and the like, constituting the controller 1(inverter apparatus) is as high as 150 degrees. Such a thermalenvironment is very hostile for these electronic components having lowheat-resistance. Therefore, the system is configured so that thecontroller 1 (inverter apparatus) is given a higher precedence over theelectric motor 2 in the cooling order, and the electric motor 2 havinghigher heat-resistance is cooled after the controller 1 (inverterapparatus), in order to achieve effective cooling with thermal balanceimproved.

According to the present embodiment, since there is provided any one ofthe above-described inverter apparatuses, that is, an inverter apparatuscapable of reducing the loss of pressure, the electric pump 4, whichforcibly circulates an antifreeze solution or water as a cooling medium,can be reduced in capacity, that is, the electric pump 4 can be reducedin size. According to this embodiment, therefore, an inexpensive coolingsystem can be provided.

FIG. 15 shows the construction of an electrical apparatus drive systemequipped with the above-described cooling system. In this embodiment,the case where any one of the above-described inverter apparatuses ismounted on an electric car, which uses an electric motor as the only onedriving source, is taken as an example. However, any one of theabove-described inverter apparatuses may instead be applied to a hybridcar, which uses an engine as an internal-combustion engine and anelectric motor, as driving sources for the vehicle.

In FIG. 15, reference numeral 39 denotes a car body. An axle 42 havingwheels 40 a and 40 b provided at the opposite ends thereof is rotatablyinstalled to the front part of the car body 39. Namely, front wheels arefixed to the front part of the car body 39. An axle 43 having wheels 41a and 41 b provided at the opposite ends thereof is rotatably installedto the rear part of the car body 39. Namely, rear wheels are fixed tothe rear part of the car body 39. An electric motor 2 is mechanicallyconnected to the axle 42 via a gear 44. An inverter apparatus 100 iselectrically connected to the electric motor 2. Direct-current powersupplied from a battery 20 as a vehicle power source is converted by theinverter apparatus 100 into three-phase alternating-current power, andis supplied to the electric motor 2. A higher-level control unit 21 iselectrically connected to the inverter apparatus 100, and inputs thecommand signal corresponding to an accelerator pedal depression amountinto the inverter apparatus 100.

According to the present embodiment, since there is provided any one ofthe above-described inverter apparatuses, that is, an inverter apparatuscapable of reducing the loss of pressure, the electric pump 4, whichconstitutes a cooling system for cooling the inverter apparatus, can bereduced in capacity, that is, the electric pump 4 can be reduced insize. According to this embodiment, therefore, an inexpensive coolingsystem can be provided. This improves the mountability of the coolingsystem onto the electric vehicle, and contributes to the reduction ofthe production cost of the electric vehicle.

According to the present invention, uniform cooling allows to beachieved without the need for accumulating parts, thereby improvingthermal characteristic, and also enables the pressure loss in the partsother than the cooling part to be reduced.

While the present invention has been described with reference to whatare at present considered to be the preferred embodiments, it is to beunderstood that various changes and modifications may be made theretowithout departing from the present invention in its broader aspects andtherefore, it is intended that the appended claims cover all suchchanges and modifications that fall within the true spirit and scope ofthe invention.

1. A direct cooling inverter comprising: a plurality of semiconductorchips; a substrate for mounting the plurality of semiconductor chips; abase for mounting the substrate; a fin formed integrally with the base;and a case having an opening part; wherein at least part of a liquidpath of a cooling medium is formed by mounting the base on the openingpart of the case; wherein the base and the fin are directly cooled bythe cooling medium; wherein the liquid path comprises a cooling partformed at the bottom of the plurality of semiconductor chips and anintroducing part for introducing the liquid medium supplied from anoutside to the cooling part; and wherein the liquid path forms asubstantially U-shape.
 2. The direct cooling inverter according to claim1, wherein the direct cooling inverter is a two inverter systemcomprising liquid paths that are serially connected into the U-shape. 3.The direct cooling inverter according to claim 2, wherein thecross-sectional area of the liquid path extending from the introducingpart up to the cooling part is substantially constant.
 4. The directcooling inverter according to claim 3, wherein the fin is formed inparallel with a longitudinal direction of the liquid path.
 5. A directcooling inverter comprising: a first module having a plurality of firstsemiconductor chips; a second module having a plurality of secondsemiconductor chips; and a case having a first opening part and a secondopening part; wherein a liquid path of a cooling medium is formed bymounting the first module on the first opening part and formed bymounting the second module on the second opening part, wherein the firstmodule and the second module are placed on the same place; and whereinthe liquid path between the first module and the second module forms asubstantially U-shape.
 6. The direct cooling inverter according to claim5, wherein the first module comprises a first substrate for mounting theplurality of the first semiconductor chips, a first base for mountingthe first substrate, and a first fin formed integrally with the firstbase, and wherein the second module comprises a second substrate formounting the plurality of the second semiconductor chips, a second basefor mounting the second substrate, and a second fin formed integrallywith the second base.